Gyrator Active Inductor Circuit for Full DC Bias Range
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Solution Overview
Problem
Active inductors face limitations due to the requirement for the gate-source voltage of transistors to exceed a threshold, restricting the operating voltage and usability, as they need to be above the nominal power supply voltage or limited to below the threshold voltage, which reduces their practical application.
Innovation Solution
The proposed solution involves gyrator-based circuits with specific transistor configurations, such as connecting resistors to the drain and gate of pMOS and nMOS transistors, and adding current sources, allowing the inductive impedance to operate over a full range of direct current bias without additional power supplies, effectively simulating inductive behavior across a wider voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate-source voltage is required to exceed threshold voltage, then transistor can operate in saturation region for amplification, but operating voltage range is restricted and usability is reduced
Solution Approach 1:
The patent inverts the conventional approach by using the transistor in the triode region instead of saturation region. The active inductor uses the transistor's triode-region characteristics with a specific biasing configuration where the gate voltage is controlled to maintain proper operation without requiring gate-source voltage to exceed the threshold voltage by a large margin. This inversion of the operating region allows the circuit to function as an inductor while expanding the usable voltage range.
Solution Approach 2:
The patent changes the operating parameters by adjusting the biasing conditions and using specific resistor configurations to set the transistor in the triode region with appropriate overdrive voltage. By changing the operating point and using degeneration resistors, the circuit achieves inductive behavior without requiring the traditional high gate-source voltage, thus expanding the operating voltage range while maintaining reliability.
2Adaptability or versatility
If additional power supplies are used to expand operating voltage range, then voltage flexibility is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent makes the single power supply serve multiple functions by using it for both the main supply voltage and generating the necessary bias voltages through resistor dividers and current mirrors. The circuit is designed to operate from a single supply voltage while internally generating all necessary bias conditions, eliminating the need for additional power supplies and reducing overall system complexity.
Solution Approach 2:
The circuit generates its own bias voltages and operating points using only the single power supply and passive components. The biasing network automatically sets the appropriate voltages for transistor operation in the triode region, and the circuit self-adjusts to maintain proper operating conditions without requiring external bias supplies or complex power management circuitry.
3Power
If transistor operates in saturation region, then high gain is achieved, but voltage headroom is reduced and operating range is limited
Solution Approach 1:
Instead of using the saturation region for high gain as in conventional designs, the patent inverts the approach by operating the transistor in the triode region where it provides variable resistance. The inductive behavior is achieved through the interaction of this variable resistance with parasitic capacitances and biasing networks, rather than through high-gain saturation operation. This inversion allows for greater voltage headroom while maintaining the necessary amplification through the inductive impedance simulation.
Data Source
AI summary
In one embodiment, a circuit, which comprises a resistor and a pMOS or cMOS transistor, has the characteristic of an inductor and produces an inductive impedance that operates over a substantially full range of a direct-current bias.